Three-dimensional (3D) television has been a technology trend in recent years that intends to bring viewers sensational viewing experience. Various technologies have been developed to enable 3D viewing and the multi-view video is a key technology for 3DTV application among others. For 3D coding, depth maps are also coded along with the texture data. In typical scenes, the correlation between the texture pictures and the depth maps is usually very high. In order to improve coding efficiency for depth maps, coding parameters for collocated texture pictures may be used for depth map coding.
In the current 3D-HEVC, the texture merging candidate is also used for depth Merge mode. In texture merging mode, motion parameters such as motion vectors (MV) and reference indices are inherited directly from the collocated block in the texture picture. FIG. 1 illustrates an example of corresponding texture block derivation. Depth block 112 in depth picture 110 corresponds to a current depth prediction unit (PU). Texture block 122 in collocated texture picture 120 corresponds to a collocated texture block. The collocated texture block (122) may be further partitioned into sub-blocks 124. If the current depth PU (112) merges with the texture merging candidate (122), the current depth PU will inherit the motion information from the collocated texture block. In the current draft 3D-HEVC, the texture merging candidate for the depth map coding is derived as follows:mvLXT[0]=(textMvLX[xRef][yRef][0]+2>>2,mvLXT[1]=(textMvLX[xRef][yRef][1]+2>>2, andrefIdxLX=textRefIdxLX[xRef][yRef].
In the above equations, mvLXT[0] and mvLXT[1] correspond to the MV candidates for the depth PU in the x and y directions. The MV candidates are determined from the MVs of the collocated texture block. Furthermore, the texture MVs is scaled down by a factor of 4 to match the spatial resolution of the depth picture since the MV for texture component has a quarter-pel resolution while the depth component has integer resolution. If the texture component and the depth component had the same resolution, there would be no need for the scaling operation.
In a coding system, it is possible for an encoder to configure the reference lists of the texture component and the depth component differently. If a reference index represents reference pictures in the texture component and the depth component with different POC or ViewId, the inherited MVs will be incorrect or inaccurate. Furthermore, such system may also result in a reference index for the texture component that is invalid for the depth component. This could cause system crash if the situation is not taken care properly.
Accordingly, it is desirable to develop a method and system that can result in reliable texture merging candidate for depth map coding. At the same time, it is desirable that the developed system can retain the performance without noticeable performance degradation.